High-frequency-electrical oscillator



J. T. RANDALL ET AL 2,542,966

HIGH-FREQUENCY ELECTRICAL OSCILLATOR Feb. 20, 1951 3 Sheets-Sheet 1 Filed Aug. 20, 1941 INVENTORS /0/21z Timidn Banded! fienryfllberi'bbwarzifiooi ATTORNEYS Feb. 20, 1951 J. T. RANDALL ET AL HIGH-FREQUENCY ELECTRICAL OSCILLATOR MAGNET/6 INVENTORS John Tarzan/Randall fienryfilberlflowardfiooi' ATTORNEYS INVENTORJ flZ/ ATTORNEYS 3 Sheets-Sheet 3 v John ThrtonEandall HenryA/bart HowaraBooi Feb. 20, 1951 J. T. RANDALL ET AL HIGH-FREQUENCY ELECTRICAL OSCILLATOR Flled Aug 20 1941 FL g5. 63.

' space.

Patented Feb. 20, 1951 2,542,936 HIGH-FREQUENCY enactment; o s-ommzrom John Tilitiifi Randall andll liiryjlbrt Howard Boot, Birmingham; England; a

lish- Electric valve company Limited, Chelins ford;- Er'igland; a company of GreatBritain nn t a u ust 4. sealin -1. 73680 In Great Britain August-22;.19

r This invention relates to highfrequehcy'electr'ical oscillators of the magnetron type.

Such magnetrons depend for their operationuponthe curvilinear motion imparted to a moving'electron by a magnetic field; electronsemitted by the cathode are thuscau'sed'to follow substantially circular or spiral paths; and various arrangements exist whereby such electrons are caused to giveup their energy to externarcircuits in whichoscillatory currents of very high frequency may thereby be induced.

It isknown that anelectron" movirig" freely under the action'of auniform magnetic field and subjected to no I otherinfiiiencewill theoretically traverse a circular path, its period of rotation being independent of its'velocityand' the radius of the circular path'buta functionof the field strength. During recent years it has been roposed, for thegenerationof ultr'a s'h'ortwav'es, to employ magnetron devices depending for their operation upon the reaction between theelectro'n stream and one or more substantially closedresthere has'liitherto been coh'sidelablefiifiiciflty obtaining large powers from maghetrons of this orother types, particularly at wavelengths below about 50 cm.-

The primary object of the presentiiiivehtidh 'is to provide a'magnetrondevice"capable of geii;

eratingshort" or ultra-short'Waves-of considerable power, and adaptable to either ooiitiniiousfwave orinterrupted continuouswavewvorking. A further object is the provision of a magnetron'c'apable' of acting as a sensitive detector of such waves. The invention is particularly applicable to systems-of the kindused for determining th'e'position' of aircraftor other objects by means of radio echoes; since such systems in general depend upon the'useoi sharply defined'beains of ultrashortwave radiation of considerable-powerj the invention is; however, by'no means confinedto this particular application, but may" also be applied to radio communication,- r'adi'o beacon systems or other purposes;

A magnetron according tothe invention is characterized'by the provision of a member cornprising the anode within which a plurality" of resonator cavities, of substantially the same natural frequency; are disposed' about and *open into a central axially disposed anode cathode The openings or gaps connectin said cavities to said space serve, when the device is in" operation, to couple'thecavities to the-space. The device is further characterized "byfthe prsence of some-or all ofa? number of" improved zs ciaims. (ornat -96) features, which serve to'incr'ease thepowe': and

efliciency of the device. Among'th'es'e may articiil'ajrly be" mentioned the" provision of means for prevehting'thejes'cap'e' of high frequendy ewetromagneticfieldirbm the device other than by the outp t eans, and of means, independent of the firstrhentioned" o enings between the resanatbr'cavities and the" aXiaIdiScharQ space; for coupling each of thefc'ajvitiesf tb an adjaeiit cavity; This additional ccuplmg' may bep'ro- Inthe" preferred construction the resonator cavities" a'ndthe central axial spaceopen; at bbth en s iiitocomnio'ri' end s aces; which serve" as continuation thereof. Closure means of "chiidu'ctupontne eXi'St'enCeOf a ielatively high degree of electromagnetic coupling between the resonators, and the feature described a ove whereby thewh'ole'of the" interiorof' the device is en'- closed asfar' as possible in a'con'diicting' envelop e isdesigned to achieve this end. If thereso'- natoi's andcentra'l space'open'e'd at'tli'eifends into s aces which were closed only" by horicondiicting rnaterial large stray eiectror'fian lietic field'would exist, and the 'degree of obliplir'igjbetween' the resoiiators would "be relatively small. Byf the arrangement described whereby the resonators and central space open at their ends into end spaces which are substantially closed by conducting material the existence of such a stray field is prevented; this arises from the fact that at the extremely high frequencies involved the induction of eddy currents in the internal surface layer of the conducting envelope prevents the magnetic field from penetrating this envelope to more than a very limited extent,

ing part. In these drawings-- Fig. 1 is an end elevation of a magnetron in 'accordancefwith the invention, the pole pieces oi the electromagnet providing the magnetic field and one of the end plates which normally cooperate with the anode in closing the magnejtron envelope being omitted in order to show the internal construction of the device;

" jFig. 2 is a side elevation of the magnetron of 'Fig. 1,. partially in' section and showing only fragments of the electromagnet pole pieces;

Fig. 3 is a longitudinal section, on an enlarged scale and With certain parts shown in full, of an indirectly heated cathode suitable for use in ,jmagnetrons of the present invention;

Fig. 4 is a sectional view, on an enlarged scale,

of a single resonator of the type shown in Figs. 1 and 2;

Fig. 5 is a sectional view of a modified form of magnetron embodying the invention particularly adapted for the generation of continuous waves, a number of the parts being omitted in the interest of simplicity;

Figs. .6 and 7 are end and side elevations, re-

spectively, similar to Figs. 1 and 2, of a modified form of magnetron embodying the invention;

Fig; 8 is a sectional view, on an enlarged scale,

of a single resonator of the type shown in Figs.

6 and 7 Fig. 9 is a fragmentary end elevation of another magnetron, showing a modified form of resonator;

Figs. 10 and 11 are fragmentary sectional views, on difierent scales, transverse to the axis of the magnetron, showing further modifications in the form of the resonator cavities; and

Referring first to Figs. 1 and 2, the magnetron illustrated therein comprises a block I, preferably of tellurium-copper alloy, having a cylindrical cavity 2 drilled therein to form the main anodecathode space the anode being fo'rmed by the block I and the cathode 3 being constructed as hereinafter described with reference to Fig. 3

and lying along the axis of the cavity 2. The resonators are formed by a plurality of further 'i'cylindrical holes or cavities 4 arranged sym- 'metrically about the cavity 2 and having their gaxes parallel to and equidistant from its axis. ,The ,wall separating each resonator from the central cavity2 is split by a relatively'narrow longitudinal slot 5 parallel to and embracing the plane defined by the axes of the cavity 2 and of the resonator in question.

The resonators 4 and central cavity 2 open at both extremities into end spaces 6 formed in the main block I; these end spaces are closed by circular copper end plates 1 sealed in a gastight manner as hereinafter described within recesses'! formed at the ends of the cylindrical walls 6' of the end spaces 6. A copper tube 8 whose axis is at right angles to that of the cavity 2 opens into each end space 6, being soldered or otherwise secured to the cylindrical wall 6 over an opening therein. The other end of each tube 8 is sealed to a thimble-shaped member 9 of heat-resisting glass, preferably of the kind known under the registered trade-mark Pyrex. Through the ends of these Pyrex thimbles are sealed tungsten rods II] which form the cathode connections, these rods passing through the copper tubes 8 and carrying at their inner ends, within the end spaces of the magnetron, the cathode mountings described below. Tubes 9' formed integrally with the walls of the Pyrex thimblesB are used during manufacture for the exhaustion of the magnetron to a very-high vacuum,.after which these tubes are sealed off.

The cathode 3, which is illustrated separately .in Fig; 3, consists of a nickel or alloy tube H coated externally with the usual oxide coating. The tube is heated by means ofatungsten spiral l2 which is a sliding fit in the tube and which is insulated from it by a coating of alumina on The cathode is supported by the ends |5-of the heater Wire l2 on to which are pinched the ends of nickel members 16 (Figs. 1 and 2); these are made of wire or strip according to the weight of the cathode and the current to be carried, and their other ends are preferably joined to the ends ofthe tungsten rods ID by arc welding in an atmosphere of hydrogen. The members l6 are of suchaform that by bending them the cathode can be adjusted to any position in the plane Of Fig. 1. r r a For the purpose of preventing or minimising the passage of stray electrons into the end spaces 6, which would diminish the efficiency, circular end shields I! (Fig. 2) of approximately the same diameter as the cavity 2 are provided a both ends of the cathode in known manner; these shields are arranged to be at cathode potential, so that they will repel any electrons approach- ,ing them back into the cavity 2. The shields I! are preferably of nickelsheet or a non-magnetic alloy such as that known under the registered trade-mark Ferry, and are provided with tags l8 attached by spot welding to the rods ill. The end shields l1 and end plates '1 are omitted ,up energy by virtue of its electromagnetic coupling with the resonator system. One end of 5. this loop passes out through ahole 20 which is drilled through the main block 1 .at right angles to the axis of the resonator, and enters the resonator at a point diametrically opposite to the slot 5 connecting the resonator to the central cavity 2; the other end of the loop is connected to the main block at a point 21 at one side of the resonator. The free end of the loop I9 is soldered to a stout tungsten wire 22 which passes through a copper tube 23 and is sealed through a Pyrex cap 24 in a manner similar to that employed for the filament connections In. Although it is located in one resonator only, the loop i9 is, by virtue of the electromagnetic couplin between the resonators, drawing energy from the whole system.

Thernagnetic field is preferably applied by means of a powerful electromagnet whose pole pieces 25 are in close proximity to, .but insulated from, the copper end plates I of the device. The field is thus substantially parallel with the axes of the resonators and the central hole. Brass cooling fins l are provided on the outer .part of the block I.

The mode of operation of the device appears to be somewhat as follows. Electrons emitted by the cathode 3 will, under the joint action of the electrostatic and magnetic fields, follow substantially spiral path in known manner. It is clear that these electrons, in passing the gaps of the resonators 4, will tend initially to induce feeble oscillations in the resonators. Now the resonators have all the same natural period of oscillation, and further, by virtue of the electromagnetic coupling between them,any given resonator is constrained to oscillate in a definite phase relationship with th adjacent resonators on each side of it. The resonators will thus tend to oscillate as a whole, and as soon as they commence to do so, the alternating fields set up across their gaps 5 will react back upon the moving electrons in the central space. The eflect of this reaction appears to be that the electrons, instead of being uniformly distributed, form themselves into concentrated circumferentially moving groups. Now if such a group approaches a resonator gap at an instant when the field across this gap is such as to oppose the motion of the electrons, it is clear that the group as a Whole will be slowed up, and will thus impart some of its energy to the oscillating system. A number of such groups of electrons, symmetrically spaced and moving with the correct angular velocity (determined by the strength of the magnetic and electric fields) are thus capable of imparting to the resonators timed impulses which will keep them in a state of continuou oscillation. The composition of these groups of electrons is, of

cour e, not constant, as superimposed upon their movement is a continuous flow of electrons from the cathode to the anode.

The above explanation should be regarded as being only tentative, as the actual conditions are very complex and apparently incapable of exact mathematical analysis. The explanation is, however, supported by the fact that theoretical design formulae based thereon have been found to form a sound guide to the operation of the device in practice.

The oscillations are preferably fed to the transmitting aerial by means of a concentric transmission line of known form which constitutes an extension of the free end of the output lead 22 and of the tube 23, which is provided with a screwed member 26 for attachment to this transmission line. The aerial may conveniently con sist of the free end of the. central .core of the transmission line, which is arranged to project a quarter wave length beyond the open end of the surrounding tube. .For directional transmission, the aerial may be inserted through the side of a large copper tube one end of which, near the aerial, is closed by an adjustable plunger serving as a reflector. Provided that the conductivity of the internal surface of this tube is kept high by making it clean and smooth, the waves may be confined within the tube in known manner without serious loss and emitted from the other end, where they maybe directed in a beam of any desired angular width by a suitably .designed horn. Alternatively transmission may be effected from a dipole aerial in known manner, in conjunction, if desired, with a parabolic reflector for directional transmission.

Consideration will now be given to the problem of designing a magnetron according to the invention to fulfill given requirements. In this connection three fundamental equations have been developed; these are:

V=potential difference betweenanode and cathode (volts).

H=magnetic field (oersteds).

P=output power (kilowatts).

D=diameter of central cavity 2 (cm.).

N=number of resonators 4.

L=axial length of resonators and, in'the form of magnetron shown in Figs. 1 and 2, axial length of cathode 3 (cm.).

A=phase difference between oscillations in adjoining resonators (radians).

W=wavelength (ems) E=efficiency (ratio of output to input power).

These equations have been developed from first principles, and are based on the hypothesis previouslyset out concerning the mode of operation of the device. It has been assumed (1) that the cathode diameter=0.4D, as in magnetron design generally this dimension has been found to provide optimum field conditions at the oathode, and (2) that the emission current density is 5 amps. per square om., which for apparatus of this general kind is usually considered to be roughly the maximum permissible value to avoid flash arcs.

In order to obtain relatively simple expressions certain further assumptions have been made; the equations must not, therefore, be taken to represent an exact mathematical analysis of the working of the device under all conditions. It is known, for example, that the emission current value given above can be almost doubled under certain conditions, and it is found thatthe device will work with increased efficiency on higher values of V and H than those given by the equations. Moreover, the cathode diameter is not necessarily confined to the value of 04D referred to above. The value of these equations resides in the fact that magnetrons designed on the basis thereof will always operate satisfactorily in accordance with the values given, and the equations therefore form a simple and useful basis for design work.

In order to make use of the equations it is necessary to know the values of A and E that will 7. obtain. If we consider the phase difference between consecutive resonators in turn until we complete the circle, it will be seen that NA must be a multiple of 21r in all cases. For any even value of N it appears that A=1r, while for odd values of N it is at present necessary to determine A experimentally for each case; thus for N :5 it has been found that under certain operative conditions A=81r/5. As regards E, this again must be determined experimentally for the particular class, of design concerned, and an estitween W and the dimensions of an individual resonator as illustrated in Fig. 4, in which d represents the diameter of'the resonator 3, w the width of the slot 5 and Z its radial depth. The

simplest fundamental calculation leads to the result where K is a constant whose value is given by Mott as 7.23; we have found this value to agree 7 reasonably well with a series of experimental results in which the observed values of W ranged from about 2 to 10 cm. An alternative method of dealing with the problem consists in the use of a series of empirical curves relating the variables involved. It may be mentioned in connection with Fig. 4 that if it is desired to obtain a very'sharp frequency response curve the values of Z and 10 should be such as to make the capacity across the slot as small as possible; in cases where this consideration is not of primary im porta-nce, however, other types of resonator not having these characteristics may be employed, as hereinafter described.

In addition to the relationships referred to above, a further purely geometrical relationship exists which is expressed in the equationwhere t is the minimum thickness of the wall between two adjacent resonators, and R is the distance between the axis of the central cavity 2 and that of any resonator. The importance of the quantity t resides in the fact that in mag.-

netrons designed to produce large powers it is desirable to make if as large as possible to aid efficient cooling; it is, however, clear that making if very large would tend to reduce the magnetic coupling between the resonators, but in designs involving large values of t it has not been apparent that this has any appreciable adverse effect.

It will be seen that the above equations define the relationships between the main factors involved in the design of a magnetron according to the invention. Given, for example, the wavelength, power output and, say, maximum permissible size and/or weight of the device, it will readily be apparent how the equations may be used to determine the optimum dimensions and approximate values of magnetic field and anode voltage that will be required.

The constructional techniques which may be employed in the manufacture of a typical magits use in high vacuum apparatus.

8 netrori as illustr'ated'in Figsl and'2 will now be briefly considered.

The anode block I is made of tellurium copper on account of its free machining properties, it

being in'this respect superior to machining brass, 7 combined with high-thermal and electrical concentral hole 2. In all'cases the holes are finished by reaming to obtain the requisite accuracy and finish. The slots 5 are cut on a slotter using a tool ground to the exact width of the slot with the work mounted on a horizontal indexing table. The endplates l are turned from arsenic-free high conductivity copper sheet to minimise the possibility of leaks occurring through their thickness. V

The side stems 8, 23 are turned from arsenic free copper bar, and the glass members 9 to which they are sealed are of glass Whose expansionp-roperties match those of the tungsten rods 50. These side stems are preferably soldered to the main block I by a silver solder or any solder free from highly volatile constituents liable to interfere subsequently with the emission or vacuum.

All parts are carefully cleaned immediately before assembly by boiling in 5% H2804 followed by cold strong chromic'acid containing a trace of H2804, and are finally rinsed in boiling distilled water.

The last parts to be assembled are the end .plates 1, which form the final closure. These are preferably sealed in place in known manner by the use of gold or tinned silver washers which are inserted between the end'plates and the main block I within the recesses 1; sufficient pressure is then applied to provide a substantially gastight closure, the device is evacuated, and finally raised to a temperature sufiicient to cause superficial alloying of the Washer with the end plate and main block. This technique avoids any oxidation or contamination of the internal surfaces during the sealing operation, and may, if desired, also be used for securing the side stems 8, 23 in position instead of using solder.

In an alternative method of effecting the final assembly the plates 1 and recesses I are tinned,

\ the whole is thoroughly cleaned, and the plates 7 and slots broached one at a time in a single pass; 7

or alternatively, in suitable cases, all together at one pass with a multi-splined broach.

Magnetrons according to the invention are adapted for use as generators of either continuous' wave 'or interrupted continuous wave oscillations, the radiation in. the latter case taking the form of a series of timed pulses. For continuous wave working, it is found that in cases where considerable power is developed the heat generatede results: in. cathodes of: the; cylindrical type shown Figs 1 and 21 becoming raised to; too high, a temperature. Themagnetron illustrated in Fig. 5, which is specially. adapted, for continuous wave working, has been designed to overcome this diflicultm In this design the cylindrical, cathode; is replaced by a disc. typecathode 3 of the indirectly heated,typelocatedwithin one ofytheend recesses 6.. The tungsten heater leads II}. are led outthrough a single tube 8 and. glass member 9; The cathode proper; may be surrounded by a focussing cylinder 3. connected, as shown, to one of the heater leads it or to a separatelead for control purposes; alternatively this focussing cylinder may be dispensed with. Cathodes such as 3 may be provided in bothof the end spaces 6, in whichv case, the heater leads maybe brought out radially, as in-Figs: 1 and 2, to reduce the overalllength. This design may also;b,eemployed in thecaseof a single cathode. The-further reference numerals inFig. 5 have the same significance as in Figs; 1 and 2;

Figs. 6, 7 and 8 illustrate a modified form of magnetron in which the resonator cavities 38 take the form of radial slots, uniform in cross section, extending about and opening into the central space 2 and having theirends opening into the two end spaces 6; as in the-device of Figs. 1 and2. The radial length of each of theslots his indicatedin Fig. 8 as Z and the-width as w. Since it may notbe practicable to include a coupling loop such as 19', Fig. 1, within one of these slots, power may be fed out through. a lead 2? which forms a direct tap at a-convenient voltage antinodal point along the end of one of the fins 41: separatingthe slots. This-lead 2-1, which is so positioned as to link a part ofthe' magnetic flux common to the-tworesonaton slots lying on opposite sidesof the nu l. to which thelead is connected, passes out through a side-tube 28 connected to the end space B as shown inFigs. 6and Z, the tube 28 being similar to thetube 23 shown in Figs. 1 and 2 and the lead 21 being connected to the outputwire 22 which is sealed through the insulating cap .24.: as previously described.

The primary. advantage of thisslotted resonator designiresides in the fact thatla large number of: resonators may be incorporated; thus: enabling relatively low values of Vand I-Ito be employed,

as will be seen from Equations I and II. Fig. 9

shows .a further. type of slotted'resonator design in which eachslot 4b terminates in a gap 5t of reduced width: in the vicinity of the central cavity 2.;

ma convenient manufacturing technique for the designs of Figs. 6 to 9: the slots 4a or 4s are first. cut radially inwards on a solid cylindrical blockwhose outer curvedsurface is indicated by 2,9. The outer endsof the fins 4 thusformed are then soldered within anannular member 3|] forming the main anode block, and the central cavity 2" is finally. drilled out. Alternatively (in the=case of Figs. 6 and-7') a single; blockmay be employed; in which thecavity 2 is first drilled, the slots .4" then being cutoutwardly from Within this cavity.

Fig. illustrates a further design. in which the fins 41 which separate the resonators 4e may conveniently be formed separately andsoldered within the annular. member 31]. Fig. 11 shows a still. further. design, in which a manufacturing technique similar: toxthe first of thosedescribed in connectionw-ith Figs. 6' to ilrnay be employed. This. technique may-also,- if desired, be usedfor the design shown in Fig. 10.

In. addition to operating at' thefundamental mode of oscillation, the resonators .41 can theoretically oscillate at the higher harmonic modes in the series I, 3; 5, etc; Consideration will now be given to the possibility of inducing such harmonic oscillationsin magnetrons according to the inven tion, and? thus obtaining extremely small wavelengths.-

0n the hypothesispreviously set out concerning the operation. of: the device, it is assumed that the electrons are formedinto groups by the action thereon of feeble oscillationsinitially induced in theresonators. It would, therefore, appear that if the resonators wereconstrained to oscillate at one ofthe higher harmonics from the outset the resulting relatively close grouping of the electrons: would besuch that, provided the groups arrived at the slots 5 ofsuccessive resonators in the correct phase, the device could be maintained in stableoscillation at this mode.

One possible method of carrying thisconception into effect is based on the provision of an even number of resonatorswhose slots are: spaced alternately X1 and X2 radians apart. Fig. 12 showssuch an arrangement, the spacing between resonators 3 I and 32 being Xi radians while that between resonators 32 and 33 is X2 radians. In all other respects, the device of Fig. 12 may be the same as that illustrated in Figs. 1 and 2. The principle of operation of this construction may briefiy be explainedas follows. Assume that the resonators have initially started to oscillate feebly at their fundamental frequency in the phase relationship determined by their electromagnetic coupling. Consider a particular group of electrons which has passed the slots of 3| and 32. in the correct phase. Owing to the difference between X1 and X2 this group will arrive late at 33 assuming that it arrives l/r of a cycle late, the stimulus it will impart to 33 will apparently-be such as totend to induce the 1th harmonic therein. Assuming further that as a result of. the coupling corresponding harmonic oscillations are induced in the other resonators, the effect of these oscillations on the electron stream will apparently be the setting up of closely spaced groups such as to maintain this mode of. oscillation.

The production of harmonic and like oscillations is not confined to the circular type of resonator shown in Fig. 12. Resonators of the slot type shown in Figs. 6 and 7 may, for example,

1 Resonators of any other formthan circular may also be split up into a number of smaller resonators.

Various constructional modifications and fur;- ther minor design details will now be considered.

In a modification-of the-cathode illustrated in Fig. 3 the heater i2 is made considerably smaller in diameter than the tube H, so that it does not touch the latter at any point, and is held under slight tension along'thecentre of the tube. The alumina coating may thus be eliminated, and this gives freedomfrom heater failures due to breakdown of this coating, which may occur if any very high current discharge takes place in the magnetron. It may be mentioned in this connection that the effects of any such flash over are greatly-minimised by-using a resistanceof about ohmsin series with the high tension supply. In cathodes of the larger sizes small pieces of nickel tube are forced into the holes .in the insulating plugs l3 and the heater wire l2 passes through these tubes. The members l6, Fig. l, are then pinched onto these tubes which are in turn flattened onto the'heater wire I2. This method is used to avoid straining the brittle heater wire with the weight of the cathode. If

desired the cathode may consist simply of a :directly heated filament, suitably coated or otherwise, or may take any other'convenient form.

'According to a modified method of mounting the end shields i1 these are connected directly to each end of the heater wire l2, after which the assembly is held in position by means of a jig and the rods [0, which are made'longer than in Fig. 2, are spot welded directly on to the end shields. and 7. According to a further method the whole assembly comprising the cathode, cathode connections and end shields if any, is mounted on a suitably formed end plate which is finally secured to the main block. Whatever method is employed forthe cathode mounting one or more suitable high frequency chokes may be used to prevent loss of oscillatory power through the heater leads. "Thecoupling loop l9, Figs. 1 and 2, may have any desired number of turns, or may be replaced by a loop located in one of the end spaces This construction is shown in Figs. 6

replaced by a direct connection to a suitable voltage antinodal point on one of the anode segments which separate the resonator cavities, as in Figs. 6. and '7, or alternatively by a capacitative coupling.

In a modified transmission system the concentric transmission line is dispensed with, the free end ofthe loop I9 being formed into a similar 100p within a bulb of glass or other non-conducting material, the interior of which is in communication with the evacuated interior of the magnetron; this second loop is inserted within a tube forming a wave guide, the axis of the tube lying in the plane of the loop.

Among further constructional and operational modifications may be mentioned the following. The air cooling system shown in Figs. 1 and 2 ma be replaced by a water cooling system, wai ter being circulated either through suitable ducts formedin the main anode block I or through external tubing. Tuning of the magnetron may.

be effected by the provision of one or more movable plates within the end spaces 6, the effect of adjusting these plates being to vary the mutual magnetic field may be applied by means of a 'permanent magnet instead of by an electromagnet as described; whichever is employed, it may be arranged withinthe body of the magnetron instead of externally as previously described. As a further alternative the magnetic field may be provided by a powerful solenoid surrounding the device; this construction is useful where large values of L are required. The main anode block need not be produced by machinin 12 as previously described; it may be formed in any other convenient manner, as for example by diecasting or by the assembling of a plurality of laminae. Further variations of the details of construction and materials employed may be made to suit particular requirements.

Dimensions and operational data of five typical magnetrons. according to the invention, denoted by the letters (a) to (e), are given below. The values of V and H are optimum values, the values of P are estimated, and those of W found'by actual measurement.

Magnetrons (a) to (d) have resonators of the type illustrated in Fig. 4. Magnetron (e), however, is of the type shown in Figs. 7 and 8, so that the dimensions D and 11 do not apply to it. The lengths (radial) Z and width w of the slots 33., Fig. 8, are given for convenience under Z and w in the table respectively. The estimates of power all refer to peak power in interrupted continuous wave or pulsed working. 0

The principal advantage of a magnetron according to the invention is the high power obtainable at very high' frequency, both on continuous and intermittent working. One of the factors contributing largely to this result is the fact that high emission currents are obtainable without difficulty, since no beam arrangement is necessary as in oscillators of the Klystron type. A further important advantage of the invention is the fact that the power may be brought out along an axis at right angles to the cathode and magnetic field, which is of great value in setting up the device in conjunction with a reflector.

Although applicable mainly as'a generator of ultra short waves, the device may be used as a sensitive detector of such waves by arranging that it is normally kept on the threshold of oscillation, and is thrown into oscillation by the incoming radiation, means being provided to quench this oscillation when the incident radiation ceases. Moreover, although primarily applicable to radio work, the device may also be applied to any other purpose for which oscillatory currents of ultra-high frequency are required.

Having now particularly described and ascer- V tained the nature of our said invention, and in what manner the same is to be performed, we declare that what we claim is:

1.- A high-frequency electrical oscillator of the magnetron type comprising an anode of conducting material having therein a plurality of electromagnetically coupled resonator cavities arranged about and each of which opens into a central space within said anode, said central space and resonator cavities opening at their ends into common end spaces at the ends of said anode, members of conducting material joined to said anode at both ends and providing therewith a substantially complete conducting envelope enclosing said resonator cavities and the chamber formed by said spaces, and a cathode in said chamber.

13 2. Apparatus as defined in claim 1, said cathode extending along the axis of said central space.

to said anode at both ends and providing -therewith a substantially complete conducting envelope enclosing said resonator cavities and the chamber, shielding means for preventing-escape of electrons from said central space to said end spaces, and means for applying potential to said shielding means.

'5. A high-frequency electrical oscillator of the magnetron type comprising an anode of conducting material having therein a plurality of 5 electromagnetically coupled resonator cavities arranged about and each of which opens into a central space within said anode, said central space and resonator cavities opening at their ends into common end spaces at the ends of said anode, members oi conducting material joined to said anode at both ends :and providing therewith a substantially complete conducting envelope enclosing said resonator cavities and the chamber formed by said spaces, a cathode in said chamber, a tube of conducting material connected to said envelope, and a cathode lead extending through said tube and connected to said cathode.

6. A high-frequency electrical oscillator of the magnetron type comprising an anode of conducting material having therein a plurality of electromagnetically coupled resonator cavities arranged about and each of which opens into a k central space within said anode, said central space and resonator cavities opening at their ends into common end spaces at the ends of said anode, members of conducting material joined to said anode at both ends and providing therewith a substantially complete conducting envelope enclosing said resonator cavities and the chamber formed by said spaces, a cathode extending along the axis of said central space,

tubes of conducting material extending radially from said envelope and communicating with said end spaces, and cathode supporting and energizing means extending through saidtu'bes and connected to the ends of said cathode.

7. A high-frequency electrical oscillator of the magnetron type comprising an anode of conducting material having therein a plurality of electromagnetically coupled resonator cavities arranged about and each of which opens into a central space within said anode, said central space and resonator cavities opening at their ends into common end spaces at the ends of said anode, members of conducting material joined to said anode at both ends and providing therewith .a substantially complete conducting envelope enclosing said resonator cavities and the chamber formed by said spaces, a cathode dis posed in an end space, ,a tube of conducting material extending axially from said envelope and communicating with said enduspace, and a cathchamber formed by said-spaces, a cathode 'in said 14 ode lead extending through said tube and connected :said cathode.

8. ,A high-frequency electrical oscillator of the magnetron type comprising an anode of conducting material, said anode having a central space and a plurality of electromagnetically coupled resonator cavities arranged about and opening :into saidicentral space, and said space being enlarged at the endsof the anode to provide end spaces into which said resonator cavities open, members of conducting material joined to said anode at its ends and providing therewith a substantially complete conducting envelope enclosing said resonator cavities and the chamber formed by said spaces, and a cathode in said chamber, successive resonator openings being spaced :circumferentially from each other by different amounts proportioned to induce desired harmonic oscillations.

9. A high-frequency electrical oscillator of the magnetron type comprising an anode of conducting material, said anode having a central space and a plurality 10f electromagnetically coupled resonator cavities arranged about and opening into said central space, and said space being enlarged at the ends of the anode to provide end spaces into which said, resonator cavities open, members of conducting ,m-aterial joined to said .anode at its ends and providing thGl'GWibh a substantially complete con-ducting envelope enclosing said resonator cavities and the chamber formed by said spaces, a cathode in said chamher, and power output means comprising a cou- 'pling *loop located within said envelope and linked with the magnetic flux. between an adjacent pair of resonators.

110. A high-frequency magnetron device comprising :an anode member having :an axially extending space therein and a'plurality of resonator cavities disposed about and opening into said space, the openings ,from said cavities into said space serving to couple said cavities to said space, a cathode axially positioned in relation to said space, means independent of said openings for coupling each of .said cavities to an adjacent one of said cavities, and means for substantially preventing escape of high-frequency electromagnetic field from said device.

11. In a high-frequency magnetron device having a central discharge space and a plurality of frequency-determining cavity resonators disposed about said dischar e space. each of said resonators .being coupled to said space by way of an opening, means, independent of said openings, :for coupling each of said resonators to an ad jacent one of said resonators, and conducting end closure means for substantially preventing escape of high-frequency electromagnetic field from said space and cavities to the atmosphere.

12. A high-frequency magnetron device comprising an anode member having an axially extending space therein and a plurality of resonator cavities disposed about and opening into said space, the openings from said cavities into said space serving to couple said cavities to said space, (said member also having a transversely extending space into which said first named space opens and to which said cavities are connected by separate openings, affording coupling means for said cavities additional to said first named openings, said spaces forming a continuous chamber, a cathode in said chamber, and closure means transverse to said first named space for substanti-a'lly preventing escape of high-rrequency electrcmagnetic held from said device.

13. A high-frequency magnetron device comprising an anode member having an axially extending space therein and a plurality of resonator cavities disposed about and opening into said space, the openings from said cavities into said space serving to couple said cavities to said space, a cathode axially positioned in.relation to said 7 space, conducting closure members extending transversely to saidspace, joined to the ends of said anode member and arranged and con: structed substantially to prevent escape of highfrequency electromagnetic field from said device, and an output connection extending into the interior of thedevice into position to link with the high-frequency magnetic flux therein.

14. A high-frequency magnetron device comprising an anode member having an axially extending space therein and a plurality of resonator cavities disposed about and opening into said space, the openings from said cavities into said space serving to couple said cavities to said space, said member also having an end space enclosed therein into which the adjacent ends of said first named space and of said cavities all open, affording coupling means for said cavities additional to said first named openings, said spaces forming a continuous chamber, a cathode in said chamber, and conducting closure means transverse to said first named space arranged and constructed for substantially preventing escape of high-frequency electromagnetic field from said device. I

15. A high-frequency magnetron device comprising an anode member having an axially extending space therein and a plurality of resonator cavities disposed about and opening into said space, the openings from said cavities into said space'serving to couple said cavities to said space, said member also having an end space enclosed therein into which the adjacent ends of said first named space and of said cavities all open, affording coupling means for said cavities additional to said first named openings, a cathode in said first named space, shielding means to prevent the escape of electrons from said first named space to said end space, and means for applying cathode potential to said shielding means.

16. A high-frequency magnetron device comprising an anode member having an axially extending space therein and a plurality of resonator cavities disposed about and opening into said space, the openings from said cavities into said space serving to couple said cavities to said space, conducting end closure means for substantially preventing escape of high-frequency electromagnetic field from said device, a cathode in said space, shielding means between said cathode and the adjacent end closure means, and means for applying potential to said shielding means.

17. An electron discharge device of the magnetron type comprising a metallic anode structure having a central space and a plurality of electromagnetically coupled resonator cavities'arranged about and opening into said central space, and a substantially cylindrically shaped hollow cathode in said central space, said anode and cathode being co-axially arranged, the spacing between the outside diameter of said cathode and the surrounding portions of said anode being less than the diameter of said cathode.

18. In a high frequency magnetron device having a plurality of spaced anode surfaces interconnected by a like plurality of open-ended cavity resonators, and in which adjacent anode surfaces and cavities. are intercoupled by high frequency electromagnetic fields existing in a-region 16 adjacent the open ends of said resonatorsmeans for withdrawing oscillatory energy from said device which comprises a conductor extending into theend space of said device and disposed adjacent said open resonator ends in a plane substantially midway between two adjacent cavities in position to link a part of the magnetic flux which is common to said resonators and to avoid linking flux which is exclusively associated with either one of said resonators singly.

19. The combination, in electromagnetic oscillation apparatus, which comprises at least. two

frequency-determining cavity resonators, said resonators having openings so juxtaposedas to provide a path from one of saidresonator's into another of'said resonators for the mutal oscillatory magnetic flux which is common to' both of said resonators, and means for abstracting .energy from said resonators without. introducing excessive asymmetry into the field patterns 01' said resonators, comprising a conductive loop disposed externally of both of said resonators and substantially midway along said path in position to link a portion of said mutual flux.

20. In combination with an electromagnetic oscillation device having at least two adjacent open-ended frequency-determining cavity resonators arranged substantially parallel to each other and separated by a conductive wall, which resonators, when the deviceisf in operation, support oscillatory electromagnetic fields which are at least partly in antiphase relation, means for abstracting energy from said device which comprises a conductor disposed inthe plane of said separating wall and beyond the end thereof which adjoins said open resonator ends in position to link a part of the magnetic fiux' which is common to said resonators and to avoid linking fiux which is exclusively associated with either one of said resonators singly. l

21. A high-frequency magnetron device comprising an anode member having an axially extending space therein and a plurality of resonator cavities disposed circumferentially about said space and opening'into the latter through axially extending slots, and a cathode axially positioned in relation to said space, successive ones in which W is the wave length of the device, K is a constant, d is the diameter of each-of said cavities ,--andfl and w arethe radial depth and width of its slot, respectively. i

23. A high-frequency magnetron device comprising an anode member having an axially extending space therein and a plurality of resonator cavities disposed circumferentially about and opening into the latter, and means for emitting and causing electrons in separated groups to travel in curved pathsiaroundsaid spacetoward the boun'ding wall thereof: constituting .theanode when subjected to a magnetic field parallel to the longitudinal axis of said device.

24. A high-frequency electrical oscillator of the magnetron type comprising an anode of conducting material, said anode having a central space and a plurality of electromagnetically coupled resonator cavities arranged about and opening into said central space, and said space being enlarged at the ends of the anode to provide end spaces into which said resonator cavities open, means including said anode forming a substantially complete conducting envelope enclosing said resonator cavities and the chamber formed by said spaces, and a cathode in said chamber.

25. A high-frequency electrical oscillator of the magnetron type comprising an anode of conducting material having therein a central space and a plurality of electromagnetically coupled resonator cavities of substantially the same natural frequency arranged symmetrically about and opening into said central space, a cathode in said central space, means including said anode forming a metallic envelope completely enclosing said resonator cavities and central space and providing spaces at the opposite ends of said anode into which said cavities and central space open, and means for withdrawing high frequency energy from the interior of said envelope.

26. A high-frequency oscillator of the magnetron type comprising an anode of conducting material having therein a cylindrical central space and a plurality of cylindrical resonator cavities of substantially the same natural frequency arranged symmetrically about said central space with their axes parallel to the axis 01' said space and each opening into said central space through a relatively small gap, a cathode in said central space, means including said anode forming a metallic envelope completely enclosing said resonator cavities and central space and providing spaces at the opposite ends of said anode into which said cavities and central space open, said cavities being electromagnetically coupled to one another by fields which traverse the end spaces, and means for withdrawing high frequency energy from the interior of said envelope.

JOHN TURTON RANDALL HENRY ALBERT HOWARD BOOT.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,063,342 Samuel Dec. 8, 1936 2,217,745 Ha'nsell Oct. 15, 1940 2,305,781 Helbig Dec. 22, 1942 FOREIGN PATENTS Number Country Date 509,102 Great Britain July 11, 1939 588,185 Great Britain May 16, 1947 

